An inducible Streptomyces gene cluster involved in aromatic compound metabolism

Streptomyces setonii (ATCC 39116) is a thermophilic soil actinomycete capable of degrading single aromatic compounds including phenol and benzoate via the ortho-cleavage pathway. Previously, a 6.3-kb S. setonii DNA fragment containing a thermophilic catechol 1,2-dioxygenase (C12O) gene was isolated and functionally overexpressed in Escherichia coli (An et al., FEMS Microbiol. Lett. 195 (2001) 17–22). Here the 6.3-kb S. setonii DNA fragment was shown to be organized into two putative divergently transcribed gene clusters with six complete and one incomplete open reading frames (ORFs). The first cluster with three ORFs showed homologies to previously known benA, benB, and benC, implying it is a part of the benzoate catabolic operon. The second cluster revealed an ortho-cleavage catechol catabolic operon with three translationally coupled ORFs (in order): catR, a putative LysR-type regulatory gene; catB, a muconate cycloisomerase gene; catA, a C12O gene. Each of these individually cloned ORFs was expressed in E. coli and identified as a distinct protein. The expression of the cloned S. setonii catechol operon was induced in Streptomyces lividans by specific single aromatic compounds including catechol, phenol, and 4-chlorophenol. A similar induction pattern was also observed using a luciferase gene-fused reporter system.